Botfly larvae are parasitic maggots that grow inside the skin of mammals, including humans. The most well-known species affecting people is Dermatobia hominis, the human botfly, found primarily in Central and South America. Unlike most parasitic insects that bite and leave, botfly larvae burrow into skin and feed there for 5 to 10 weeks, breathing through a small hole in the host’s skin while they mature.
How Botfly Larvae Get Under Your Skin
The transmission method is one of the strangest in the insect world. Adult botflies don’t land on you directly. Instead, a female botfly captures a mosquito mid-flight and glues her eggs to the mosquito’s body. When that mosquito later lands on a person or animal to feed, the body heat triggers the botfly eggs to hatch. The tiny larvae then drop onto the skin and either crawl into the mosquito’s bite wound or burrow through the skin on their own.
This hitchhiking strategy is called phoresy, and it exists because the adult botfly is large, loud, and conspicuous. A person would easily swat it away. By outsourcing delivery to a mosquito, the botfly avoids detection entirely. Other biting flies can serve as carriers too, not just mosquitoes.
What the Larvae Look Like
Once inside the skin, botfly larvae grow in a pocket of tissue just below the surface. Their bodies are soft but covered in rows of hard, backward-pointing spines. These spines serve two purposes: they anchor the larva firmly inside its pocket so it can’t be easily pulled out, and they help scrape nutrients from surrounding tissue. This spine arrangement is also why removal can be tricky. If the larva breaks apart during extraction, the spines make it difficult to pull out the remaining pieces.
A mature larva can grow to roughly the size of a large peanut before it’s ready to leave. At the skin’s surface, you’ll see a small opening, sometimes called a breathing pore, that the larva uses to take in air while it feeds beneath the skin.
The Full Life Cycle
The botfly goes through six distinct stages. Adults are free-living flies that don’t feed on hosts at all. After mating, the female captures a blood-sucking insect and attaches her eggs to it. Once those eggs reach a warm-blooded host and hatch, the larvae penetrate the skin and settle into a cavity just underneath. They feed there for 5 to 10 weeks, growing through several molts.
When fully mature, the larvae tend to exit during nighttime or early morning, likely to avoid drying out in the heat. They drop to the ground and burrow into soil, where they pupate. About a month later, an adult fly emerges to mate and start the cycle again.
What an Infestation Feels Like
The medical term for a botfly larva living in your skin is furuncular myiasis. The primary sign is a growing lump that looks similar to a boil or large pimple, with a small central opening. You may notice intermittent sharp or stinging pain as the larva moves or feeds. Some people report feeling distinct movement inside the lump, particularly at night when the larva shifts position near the breathing pore.
The lump gradually enlarges over weeks. Larvae generally stay in one spot and don’t migrate through the body. The area around the lump often becomes red and inflamed, and there may be occasional drainage of clear or slightly bloody fluid from the central opening.
Which Animals Are Affected
Humans are not the botfly’s preferred host. The natural targets for many botfly species are rodents, rabbits, and hares. Domestic animals, especially cats, can also become hosts. Different botfly species have evolved for different animal hosts. Some target cattle (warble flies), others infest the nasal passages of sheep and deer (nose bots), and certain North American species in the Cuterebra genus primarily parasitize rodents and rabbits but occasionally end up in pets.
How Botfly Larvae Are Removed
There are both surgical and non-surgical approaches. The simplest non-surgical method involves covering the breathing pore with something airtight, like petroleum jelly, paraffin oil, or even a thick layer of pork fat. The idea is to cut off the larva’s oxygen supply, forcing it to move closer to the surface where it can be grasped and pulled out. A clinician may also numb the area with a local anesthetic and use a small circular cutting tool to create an opening wide enough for extraction.
The suffocation method has a significant drawback. If the larva dies beneath the skin before it can be removed, those backward-pointing spines make extraction much harder. A dead larva can’t be coaxed to the surface, and pulling it out risks tearing it apart, which can lead to infection or a prolonged inflammatory reaction. For this reason, having a healthcare provider remove the larva intact is generally the better option. The wound typically heals well once the larva is fully removed, since the body’s immune response resolves once the parasite is gone.
Where Botflies Are Found
The human botfly, Dermatobia hominis, is endemic to tropical and subtropical regions of Central and South America, from southern Mexico through northern Argentina. Most human cases in the United States, Canada, and Europe involve travelers returning from these areas. The flies thrive in warm, humid, forested environments where both they and their mosquito carriers are abundant.
North America has its own botfly species in the Cuterebra genus, but these rarely infest humans. They’re more commonly found in rodents, rabbits, and occasionally outdoor cats and dogs, particularly in the northeastern United States.
Preventing Botfly Infestation
Because botfly larvae reach you via mosquito bites, prevention comes down to avoiding mosquito bites in endemic areas. EPA-registered insect repellents applied to exposed skin are the first line of defense. Wearing long sleeves and long pants in forested tropical areas reduces the skin available to biting insects. Sleeping under bed nets and keeping windows screened also help, since the mosquitoes carrying botfly eggs behave like any other mosquitoes seeking a blood meal.
Drying clothes on high heat after washing (rather than hanging them outdoors in tropical regions) can also reduce risk, since some related fly species lay eggs directly on damp fabric. For travelers heading to Central or South American forests, the combination of repellent and protective clothing is the most practical approach.